DESCRIPTION: The overall goal of this project is to understand how polyamines regulate the susceptibility of epithelial tissues to carcinogenesis. During the last funding period, the concept that upregulation of polyamine biosynthesis would increase susceptibility of mouse skin to initiating carcinogens was established using transgenic animals in which ornithine decarboxylase (ODC) was overexpressed in specific keratinocyte populations in the skin. The proposed project period will further exploit the transgenic models to characterize the target cell for carcinogens in skin, gain insights into how polyamines enhance susceptibility to carcinogenesis, and to determine if polyamine-driven tumor promotion occurs in other epithelia. To accomplish this goal, the following specific aims are proposed: 1. Further characterization of the target cell for carcinogens in skin. This aim will attempt to prove conclusively that stem cells restricted to hair follicles are the only target cells for DMBA-initiated cancer in the skin and to answer the question: Is overexpression of ODC a necessary event in phorbol ester-driven tumor promotion? 2. Investigation of mechanism(s) of polyamine-mediated susceptibility to carcinogenesis. This aim will utilize three distinct approaches to gain insight into how polyamines enhance susceptibility to carcinogenesis. To accomplish this goal, the following approaches will be employed: a) analysis of mutation frequency and mutational spectra in vivo (using the Big Blue mouse model) after carcinogen treatment; b) characteri-zation of a modifier locus in FVB/N mice that reduces polyamine-dependent susceptibility; and c) analysis of differential gene expression in tumors under high vs. low polyamine conditions using SAGE (serial analysis of gene expression). 3. Determine the sensitivity of other epithelia to polyamine-driven tumor promotion, namely, upper digestive tract and colon, using the established ODC overexpressor transgenic mouse models, K6/ODC and K5/ODC, and two relatively organ-specific carcinogens, NMBA (N-nitrosomethyl-benzylamine) and DMH (1,2 dimethylhydrazine), respectively.